1. Field of the Invention
The present invention relates to a resin composition for extruded forms that has improved workability, and excellent properties with respect to transparency, heat resistance, low-temperature resistance, impact strength, heat sealability, food sanitation, etc., and that may particularly be advantageously used for the formation of extruded forms such as films or sheets.
2. Description of the Related Art
Hitherto, a polypropylene resin has been known as a material for forming extruded forms, such as films and sheets, which are transparent. Since a film formed of a polypropylene (hereinafter abbreviated as xe2x80x9cPPxe2x80x9d) resin also has good rigidity, etc., a PP film is widely used as a wrapping/packaging material for various applications. However, the range of fields to which a PP film can be applied is limited by the fact that the film is unsuitable for forming by a general working technique, such as air-cooled inflation forming, and that the film has poor properties with respect to impact strength, low-temperature resistance and low-temperature heat sealability.
In view of these problems, a high-pressure low-density polyethylene (hereinafter abbreviated as xe2x80x9cLDPExe2x80x9d), which is a resin capable of compensating for the problems of PP resin, has become widely used for the production of a general-use film. However, though LDPE is effective for the compensation of the problems of PP, LDPE has poorer transparency than PP.
A copolymer of ethylene and xcex1-olefin obtained by using a Ziegler catalyst in a method described, e.g., in Japanese Patent Publication No. 56-18132, is known as a linear low-density polyethylene (hereinafter abbreviated as xe2x80x9cLLDPExe2x80x9d). LLDPE is a resin having better properties than an LDPE resin, described above, with respect to impact strength, heat sealability, hot tack, heat resistance, low-temperature resistance, etc. It is known that the transparency of LLDPE can be improved by subjecting it to special working by a certain technique, such as known T-die forming, water-cooled inflation forming, or air-cooled inflation forming using a special air ring.
However, when the surface of an LLDPE film is smoothed to produce a film having good transparency, the LLDPE has its low-crystallinity components bled out to the surface of the film (this phenomenon is referred to as bleedout). As a result, the anti-blocking property of the film is greatly impaired, making actual use of the film difficult.
In order to overcome these problems, a method of adding an anti-blocking agent or slip agent, such as silica or talc, to LLDPE has been adopted. However, the addition of such an anti-blocking agent involves scattering of light, resulting in impaired transparency. Thus, it has been difficult to improve the transparency of the LLDPE resin itself.
Recently, it has become possible to obtain LLDPE having a chemical composition variation range more limited than more conventional LLDPE by using a novel catalyst described in Japanese Patent Laid-Open No. 58-19309, etc. Hence, it has become possible for LLDPE to have better transparency and anti-blocking property than a more conventional LLDPE. However, the range of molecular-weight distribution is also narrowed, thereby greatly deteriorating workability.
Further, although such a conventional LLDPE has better heat resistance and low-temperature resistance than a pp or a low-density polyethylene, the conventional LLDPE has not been quite applicable to uses such as containers for pharmaceutical products or containers for cryogenic preservation, which containers must be transparent enough to be able to preserve contents in their readily visible state or must be free from breakage when at sterilized high-temperature and used for freeze-preservation at a temperature of xe2x88x9250(copyright) or lower, and more recently, at a temperature of xe2x88x9280(copyright) or lower.
An object of the present invention is to provide a resin composition for forming extruded forms, in particular, films or sheets, that has good workability, and also has greatly improved properties with respect to transparency, heat resistance, low-temperature resistance, etc.
The present inventors have made various studies to obtain means for achieving a well-balanced material that has improved workability and that also assures excellent properties, finding that the object of the present invention can be achieved by blending together an LDPE having specific properties and an LLDPE having specific properties. The present invention has been formulated on the basis of the above knowledge.
A resin composition for extruded forms according to the present invention is characterized in that the resin composition contains component A and component B specified as follows:
Component A:
Component A is a copolymer of ethylene and olefin having a carbon number of 4 to 40, the component A being contained in the resin composition in an amount of 50 to 99% by weight, and having the following properties (a) to (d):
(a) a melt flow rate (MFR) of 0.1 to 5 g/10 min.;
(b) a density D of 0.88 to 0.925 g/cm3;
(c) an elution curve having a single peak of elution volume, as indicated by an elution curve obtained by temperature rising elution fractionation (TREF), said the peak corresponding to a temperature within a range from 30 to 100(copyright), and the elution curve satisfying a relationship in which the ratio H/W is not less than 1 when H represents the height of the peak and W represents the width of the elution curve at half of the height H; and
(d) an elution volume Y (in % of the weight thereof with respect to the total weight of the component A) at an elution temperature of 50(copyright) in temperature rising elution fractionation, said elution volume Y satisfying the following condition {circle around (1)} or {circle around (2)}:
{circle around (1)} Yxe2x89xa6xe2x88x924500D+4105 when the density D of the component A is less than 0.91 g/cm3, but Yxe2x89xa6100; or
{circle around (2)} Yxe2x89xa610 when the density D of the component A is not less than 0.91 g/cm3.
Component B:
Component B is an ethylene-containing polymer, the component B being contained in the resin composition in an amount of 1 to 50% by weight, and having the following properties (axe2x80x2) to (dxe2x80x2):
(axe2x80x2) a melt flow rate of 0.1 to 20 g/10 min.;
(bxe2x80x2) a density of 0.88 to 0.93 g/cm3;
(cxe2x80x2) a memory effect (ME) of not less than 1.3; and
(dxe2x80x2) a melt tension (MT) of not less than 1.0 g.
(1) Componenet A (Copolymer of Ethylene and xcex1-Olefin Having 4 to 40 Carbons)
(a) Properties of Component A
It is important that a copolymer of ethylene and xcex1-olefin having 4 to 40 carbons (such olefin will be referred to as xe2x80x9cC4 to C40 xcex1-olefinxe2x80x9d unless otherwise specified) contained as component A in a resin composition for extruded forms according to the present invention have the following properties {circle around (1)} to {circle around (4)}, preferably {circle around (1)} to {circle around (5)}:
{circle around (1)} Melt Flow Rate
The copolymer of ethylene and C4 to C40 xcex1-olefin used in the present invention should have a melt flow rate (MFR) within a range of from 0.1 to 5 g/10 min. as measured in accordance with Japanese Industrial Standards (JIS) K7210, preferably from 0.3 to 4 g/10 min., and more preferably from 0.7 to 3.5 g/10 min.
If the melt flow rate of the copolymer exceeds the upper limit of the range of from 0.1 to 5 g/10 min., heat resistance and low-temperature resistance may be impaired, and film formation may become unstable. A melt flow rate less than the lower limit of this range is not practical because resin pressure may become so great as to impair formability or reduce producibility.
{circle around (2)} Density
The copolymer of ethylene and C4 to C40 xcex1-olefin used in the present invention should have a density D within a range of from 0.88 to 0.925 g/cm3 as measured in accordance with JIS K7112, preferably from 0.89 to 0.92 g/cm3, and more preferably from 0.90 to 0.915 g/cm3.
If the density of the copolymer exceeds 0.925 g/cm3, transparency and heat sealability may be impaired. If the copolymer has too small a density, heat resistance may be impaired or blocking may occur on the surface of a formed film, thereby rendering the film unusable.
{circle around (3)} Temperature at the Peak of Elution Curve Obtained by Temperature Rising Elution Fractionation
The copolymer of ethylene and C4 to C40 xcex1-olefin used in the present invention should have a single peak elution curve as obtained by temperature rising elution fractionation (TREF). The peak should correspond to a temperature within a range of from 30 to 100(copyright), preferably from 35 to 85(copyright), and more preferably from 40 to 70(copyright). The elution curve should satisfy a relationship in which the ratio H/W of the height H of the peak with respect to the width W of the elution curve at half of the height H is not less than 1, preferably within a range of from 1 to 20, more preferably from 1 to 15, and most preferably from 1 to 10.
If the peak of the elution curve corresponds to a temperature exceeding 100(copyright), a formed product may have poor transparency and poor low-temperature heat sealability, thereby becoming unusable. If the peak of the elution curve corresponds to a temperature less than 30(copyright), a formed product may suffer from bleedout, and a film may suffer from blocking, thereby becoming unusable.
If the ratio H/W is less than 1, a formed product may suffer from bleedout. In addition, the copolymer may contain a not negligible amount of components that cause blocking, and a film may have impaired heat sealability after the passage of a long time, thereby becoming unusable.
{circle around (4)} Elution Volume at Elution Temperature of 50(copyright) in Temperature Rising Elution Fractionation
The copolymer of ethylene and C4 to C40 xcex1-olefin used in the present invention should have a specific elution volume Y (in % of the weight thereof with respect to the total weight of the component A) at an elution temperature of 50(copyright) in temperature rising elution fractionation, the elution volume Y satisfying the following condition 1) or 2):
1) Yxe2x89xa6xe2x88x924500D+4105, preferably Yxe2x89xa6xe2x88x924650D +4238, when the density D of the component A is less than 0.91 g/cm3, but Yxe2x89xa6100; or
2) Yxe2x89xa610, preferably Yxe2x89xa67, when the density D of the component A is not less than 0.91 g/cm3.
Obtaining Elution Curve by Temperature Rising Elution Fractionation
The elution volume of the copolymer is measured by temperature rising elution fractionation (TREF) performed in the following manner on the basis of the principles described in, for example, xe2x80x9cJournal of Applied Polymer Sciencexe2x80x9d (Vol. 26, pages 4217 to 4231, 1981) or xe2x80x9cDrafts for Symposium on Polymerxe2x80x9d (2P1C09, 1985).
In principle, TREF of a polymer is performed as follows: a polymer to be measured is completely dissolved in a solvent. Thereafter, the resulting solution is cooled, so that a thin polymer layer is formed on the surface of an inactive carrier. In the polymer layer, those components of the polymer which crystallize easily are on the inner side (the side of the layer close to the surface of the inactive carrier) while components which do not crystallize easily are on the outer side.
When temperature is raised continuously or in a stepwise manner, elution occurs, starting with the non-crystalline components of the relevant polymer, that is, those short-chain branches of the polymer having relatively high degrees of branching, these polymer components being eluted in low-temperature stages. As the temperature increases, those portions having lower branching degrees are eluted gradually. Finally, the branchless straight-chain portion is eluted, thereby completing TREF.
The concentrations of fractions eluted at each temperature are detected, and each elution volume is plotted against elution temperatures to obtain an elution curve in a graphical representation. Such an elution curve enables the component distribution of the polymer to be determined.
{circle around (5)} Q Value
The copolymer of ethylene and C4 to C40 xcex1-olefin used in the present invention should preferably have a specific Q value (the ratio Mw/Mn of the weight-average molecular weight Mw with respect to the number-average molecular weight Mn) obtained by size exclusion chromatography (SEC), the Q value being not more than 4, preferably not more than 3, and more preferably not more than 2.5.
If the Q value of the copolymer is greater than the above-specified value, the external appearance of a formed product tends to be impaired.
(b) Preparation of Copolymer of Ethylene and C4 to C40 xcex1-Olefin
A copolymer of ethylene and C4 to C40 xcex1-olefin used in the present invention may be prepared by copolymerizing the main component, ethylene, and the sub-component, xcex1-olefin, by using a metallocene catalyst, in particular, a metallocene-alumoxane catalyst or a catalyst such as that disclosed, e.g., in International Patent Laid-Open No. WO92/01723, comprising a mixture of a metallocene compound and a compound, such as one described below capable of forming a stable anion by reacting with a metallocene compound. A preparation method disclosed, for example, in any of the following publications may be used: Japanese Patent Laid-Open Nos. 58-19309, 59-95292, 60-35005, 60-35006, 60-35007, 60-35008, 60-35009, 61-130314, and 3-163088; European Patent Laid-Open No. 420436; U.S. Pat. No. 5,055,438; and International Patent Laid-Open No. WO91/04257.
The above-stated compound capable of forming a stable anion by reacting with a metallocene compound is either an ionic compound having ion pairs of cations and anions, or an electrophilic compound. Such a compound forms a stable ion by reacting with a metallocene compound, thereby providing an active species for polymerization.
The above ionic compound is expressed by the following general formula (I):
[Q]m+ [Y]mxe2x88x92 (m being an integer of 1 or greater)xe2x80x83xe2x80x83(I)
In the formula (I), Q represents a cation component of the ionic compound. The cation component may be, for example, carbonium cation, tropylium cation, ammonium cation, oxonium cation, sulfonium cation or phosphonium cation. Also, the cation component may be a metallic cation or an organometallic cation, which cation itself can be easily reduced.
The cation component may be a cation which can give away proton(s), as disclosed in Japanese Patent Publication No. 1-501950, or a cation which does not give away proton(s). Specific examples of cations of the second type include triphenylcarbonium, diphenylcarbonium, cycloheptatrienium, indenium, triethylammonium, tripropylammonium, tributylammonium, N,N-dimethylanilinium, dipropylammonium, dicyclohexylammonium, tripheylphosphonium, trimethylphosphonium, tri(dimethylphenyl)phosphonium, tri(methylphenyl)phosphonium, triphenylsulfonium, triphenyloxonium, triethyloxonium, pyrylium, silver ion, gold ion, platinum ion, palladium ion, mercury ion, and ferrocenium ion.
In the above formula (I), Y represents an anion component of the ionic compound which is transformed into a stable anion through reaction with a metallocene compound. The anion component may be, for example, organic boron compound anion, organic aluminum compound anion, organic gallium compound anion, organic phosphorus compound anion, organic arsenic compound anion or organic antimony compound anion. Specific examples of such anions include tetraphenyl boron, tetrakis(3,4,5-trifluorophenyl) boron, tetrakis(3,5-di(trifluoromethyl)phenyl) boron, tetrakis(3,5-(t-butyl)phenyl) boron, tetrakis(pentafluorophenyl) boron, tetraphenyl aluminum, tetrakis(3,4,5-trifluorophenyl) aluminum, tetrakis(3,5-di(trifluoromethyl)phenyl) aluminum, tetrakis(3,5-di(t-butyl)phenyl) aluminum, tetrakis(pentafluorophenyl) aluminum, tetraphenyl gallium, tetrakis(3,4,5-trifluorophenyl) gallium, tetrakis(3,5-di(trifluoromethyl) phenyl gallium, tetrakis(3,5-di(t-butyl)phenyl) gallium, tetrakis(pentafluorophenyl) gallium, tetraphenyl phosphorus, tetrakis(pentafluorophenyl) phosphorus, tetraphenyl arsenic, tetrakis(pentafluorophenyl) arsenic, tetraphenyl antimony, tetrakis(pentafluorophenyl) antimony, decaborate, undecaborate, carbadodecaborate, and decachlorodecaborate.
As stated above, an electrophilic compound may be used instead of an ionic compound, the electrophilic compound comprising a certain kind of Lewis acid capable of forming a stable anion by reacting with a metallocene compound so as to provide an active species for polymerization. The electrophilic compound may be, for example, a halogenated metal compound of varying type, or a metal oxide known as a solid acid. Specifically, halogenated magnesium, inorganic oxides of the Lewis-acid type, or the like may be used.
xcex1-Olefin
xcex1-olefin having a carbon number of 4 to 40, which serves as the sub-component of the copolymer, may comprise, for example, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4-methylpentene-1, 4-methylhexene-1, 4,4-dimethylpentene-1, or octadecene. Among olefins having a carbon number of 4 to-40, those having a carbon number of 4 to 18 are preferable, those having a carbon number of 4 to 12 are more preferable, and those having a carbon number of 6 to 10 are most preferable. It is preferable that 2 to 60% by weight (percentages by weight will hereinafter be abbreviated to wt %), preferably 5 to 50 wt %, of one or more such olefins be copolymerized with 40 to 98 wt %, preferably 50 to 95 wt %, of ethylene.
Copolymerization of Ethylene and C4 to C4 0 xcex1-Olefin
Methods which may be used to copolymerize ethylene and C4 to C40 xcex1-olefin comprises, for example, gaseous phase methods, slurry methods, solution methods or high-pressure ion polymerization methods. Among these, solution methods and high-pressure ion polymerization methods are preferable, with preparation by high-pressure ion polymerization methods being particularly preferable.
The above-mentioned high-pressure ion polymerization method is a method for continuous production of an ethylene-based polymer, such as that disclosed, e.g., in Japanese Patent Laid-Open No. 56-18607 or 58-225106, and the method adopts reaction conditions comprising a pressure of not less than 200 kg/cm2, preferably a pressure within a range of from 300 to 2000 kg/cm2, and a temperature of not less than 125(copyright), preferably a temperature within a range of from 130 to 250(copyright), and more preferably from 150 to 200(copyright).
(2) Component B (Ethylene-containing Polymer)
(a) Properties of Component B
It is important that the ethylene-containing polymer serving as component B of a resin composition for extruded forms according to the present invention have the following properties {circle around (1)} to {circle around (3)}, preferably {circle around (1)} to {circle around (6)}:
{circle around (1)} Melt Flow Rate
The ethylene-containing polymer used in the present invention should have a melt flow rate (MFR) within a range from 0.1 to 20 g/10 min. as measured in accordance with Japanese Industrial Standards (JIS) K7210, preferably from 0.5 to 10 g/10 min., and more preferably from 1.0 to 5.0 g/10 min.
If the melt flow rate of the ethylene-containing polymer exceeds the upper limit of the range of from 0.1 to 20 g/10 min., formability may be impaired, making film formation unstable. If the melt flow rate is less than the lower limit of this range, extrudability as well as the external appearance of a formed product may be impaired or spoiled.
{circle around (2)} Density
The ethylene-containing polymer used in the present invention should have a density within a range of from 0.88 to 0.93 g/cm3 as measured in accordance with JIS K7112, preferably from 0.915 to 0.93 g/cm3, more preferably from 0.918 to 0.927 g/cm3, and most preferably from 0.919 to 0.923 g/cm3.
If the density of the ethylene-containing polymer exceeds the upper limit of the range of from 0.88 to 0.93 g/cm3, transparency as well as low-temperature heat sealability may be impaired. If that density is smaller than the lower limit of this range, a formed product may suffer from bleedout, and a film may have a surface suffering from blocking.
{circle around (3)} Memory Effect (ME)
The ethylene-containing polymer used in the present invention should have a memory effect (3 grams) of not less than 1.3, preferably not less than 1.6, more preferably not less than 2.0, and most preferably not less than 2.3.
A memory effect lower than 1.3 is not preferable because this may cause unstable formability.
Memory effect (3 grams) is measured in the following manner by using a melt indexer such as that used in JIS K7210, and by setting measurement conditions comprising a cylinder temperature of 240(copyright), and a constant rate extrusion amount of 3 g/min:
The desired sample is charged into the apparatus, and only the piston is placed on the sample. After 6 minutes have passed, the prescribed extrusion rate is applied. Then, a graduated cylinder containing ethyl alcohol is placed immediately below the orifice of the die, so that a straight extrudate can be collected.
The diameter D1 of the collected extrudate is measured with a micrometer, and the memory effect ME of the sample is calculated by the following formula where the diameter of the orifice is represented as D0:
ME=D1/D0
{circle around (4)} Q Value
The ethylene-containing polymer used in the present invention should preferably have a specific Q value (the ratio Mw/Mn of the weight-average molecular weight Mw with respect to the number-average molecular weight Mn) obtained by size exclusion chromatography (SEC), the Q value being within a range from 5 to 30, preferably from 7 to 25, and more preferably from 10 to 20.
If the Q value of the ethylene-containing polymer is greater than 30, the external appearance of a formed product tends to be impaired. Too small a Q value is not preferable either, because formability tends to be unstable.
{circle around (5)} Melt Tension (MT; Melt Tension at Fracture)
The ethylene-containing polymer used in the present invention should preferably have a melt tension of not less than 1.0 g, preferably not less than 1.5 g, more preferably not less than 2.5 g, and most preferably not less than 5 g. Too small a melt tension is not preferable because it causes unstable formability.
{circle around (6)} Interrelationship between ME and MT
The ethylene-containing polymer used in the present invention should preferably have the following interrelationship between ME and MT:
MExe2x89xa7[0.05xc3x97MT+1.3]/g,
preferably MExe2x89xa7[0.05xc3x97MT+1.5]/g
Satisfying the above interrelationship is effective for improving workability during forming.
(b) Specific Examples of Ethylene-containing Polymer Which May Be Used
An ethylene-containing polymer to be used may be suitably selected from among substances such as polyethylene, ethylene-xcex1-olefin copolymer different from component A, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-xcex1-olefin-diene copolymer so long as a selected substance has the above-described properties. Among these substances, a high-pressure low-density polyethylene is preferably used, and particularly preferable is the use of a high-pressure radical-polymerized low-density polyethylene produced by an autoclave method in which polymerization is effected at a reaction temperature of not less than 220(copyright) under a reaction pressure of not more than 1700 kg/cm2.
(1) Properties of Resin Composition
A resin composition for extruded forms according to the present invention obtained as described above should preferably have the following properties: a melt flow rate within a range of from 0.5 to 10 g/10 min. as measured in accordance with JIS K7210, preferably from 1 to 8 g/10 min., and more preferably from 2 to 5 g/10 min.; a density within a range of from 0.88 to 0.925 g/cm3, preferably from 0.89 to 0.92 g/cm3, and more preferably from 0.90 to 0.915 g/cm3; a memory effect (ME) within a range from 1.0 to 2.0, preferably from 1.1 to 1.8, and more preferably from 1.2 to 1.6; and a melt tension (MT: stress at 50 m/min.) within a range of from 0.3 to 10 g, preferably from 0.5 to 5 g, and more preferably from 1 to 5 g.
The memory effect ME and the melt tension MT (stress at 50 m/min.) of the resin composition preferably satisfies the following interrelationship:
MExe2x89xa7[0.08xc3x97MT+1]/g,
preferably MExe2x89xa7[0.2xc3x97MT+1.1]/g
(2) Proportion of Components A and B
A copolymer of ethylene and C4 to C40 xcex1-olefin, serving as component A, and an ethylene-containing polymer, serving as component B, should be contained in a resin composition according to the present invention in an amount of 50 to 99% and an amount of 1 to 50%, respectively, both with respect to the total weight of the resin composition. Preferably, component A is contained in an amount of 75 to 99 wt % while component B is contained in an amount of 1 to 25 wt %. More preferably, these components A and B are contained in an amount of 80 to 97 wt % and an amount of 3 to 20 wt %, respectively, and most preferably, in an amount of 85 to 95 wt % and an amount of 5 to 15 wt %, respectively.
If component A is contained in too small an amount, properties such as heat sealability and transparency are impaired. If component B is contained in too small an amount, workability cannot be improved sufficiently.
(1) Mixing
A resin composition for extruded forms according to the present invention is produced by suitably mixing together a copolymer of ethylene and C4 to C40 xcex1-olefin, serving as component A, and an ethylene-containing polymer, serving as component B. For this purpose, a method similar to a conventional method for the production of a resin composition may be used.
Specifically, component A and component B are melted and kneaded together by using an extruder, a Brabender Plastograph, a Banbury mixer, a kneader-blender or the like, to thereby obtain a resin composition according to the present invention. The thus obtained resin composition is normally formed into pellets by a commonly used method. The pellets may be used to form films or the like.
(2) Other Additives
A resin composition for extruded forms according to the present invention may contain auxiliary additives generally used in a resin composition, such as antioxidants (preferable examples of which are phenol-type and phosphorus-type antioxidants), anti-blocking agents, slip agents, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizers, anti-fogging agents, and/or colorants.
A resin composition according to the present invention may preferably contain, in addition to component A and component B, antioxidants, anti-blocking agents and slip agents as component C, component D, and component E, respectively. It is preferable that these components C, D and E comprise the substances described below, and be contained in the specific amounts described below.
{circle around (1)} Antioxidant
An antioxidant added to a resin composition according to the invention may comprise a phenol antioxidant, or a phosphorus antioxidant, or both. A mixture of a phenol antioxidant and a phosphorus antioxidant is preferable.
(i) Specific examples of usable phenol antioxidants include: octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) benzene, 1,3,5-tris-[ethylene-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]-s-triazine-2,4,6-(1H,3H,5H) trione, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenol) butane, 4,4-methylene-bis(2,6-di-t-butylphenol), hexamethylene glycol-bis[xcex2-(3,5-di-t-butyl-4-hydroxyphenol) propionate], 6-(4-hydroxy-3,5-di-t-butylanilino) 2,4-bis-octyl-thio-1,3,5-triazole, 2,2-thio[diethyl-bis-3(3,5-di-t-butyl-4-hydroxyphenol) propionate], 2,2-methylene-bis(4-methyl-6-t-nonylphenol), 2,6-bis-(2-hydroxy-3-t-butyl-5-methylbenzoyl)-4-methylphenol, and tris[xcex2-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl-oxyethyl] isocyanurate. A single one of these substances, or a mixture thereof may be used. A phenol antioxidant having an alkyl group in the molecular structure thereof and also having a melting point of 40C or higher is preferable.
(ii) A phosphorus antioxidant which may be used in the present invention comprises at least one phosphorus compound selected from the group consisting of phosphites, phosphonites and phosphonic acid derivatives.
Specific examples of usable phosphites include triphenyl phosphite, diphenyl phosphite, didecyl phosphite, tridecyl phosphite, trioctyl phosphite, tridodecyl phosphite, trioctadecyl phosphite, trinonylphenyl phosphite, tridodecyl trithiophosphite, distearyl pentaerythritol diphosphite, 4,4-butylidene bis(3-methyl-6-t-butylphenylditridecyl) phosphite, tris(2,4-di-t-butylphenyl) phosphite, and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite. Other such examples include 4,4-isopropylidene diphenyltetraalkyl diphosphite having an alkyl group with 12 to 15 carbons.
Usable examples of phosphonites include tetrakis(2,4-dialkylphenyl)-4,4-biphenylene diphosphonite having an alkyl group with 1 to 30 carbons. Among these substances, tetrakis(2,4-di-t-butylphenyl)-4,4-biphenylene diphosphonite is particularly preferable.
Phosphonic acid derivatives are expressed by the following general formula (II): 
where R1 represents hydrogen, a metal, or a straight-chain or branched alkyl group having 1 to 22 carbons, and R2 represents a lower alkyl group having 1 to 6 carbons, preferably a tertiary butyl group.
Specific examples of usable phosphonic acid derivatives include calcium salts of 4-hydroxy-3,5-di-t-butyl-benzyl phosphonic acid, o-ethyl-(4-hydroxy-3,5-di-t-butylbenzyl) phosphonic acid, o-(2-ethylhexyl)-(4-hydroxy-3,5-di-t-butylbenzyl) phosphonic acid, and o-ethyl-(4-hydroxy-3,5-t-butylbenzyl) phosphonic acid.
Among the above-listed examples of phosphorus antioxidents, a phosphorus antioxidant having a melting point of 60(copyright) or higher is preferable. More preferable is a phosphite or a phosphonite, and most preferable is tris(2,4-di-t-butylphenyl) phosphite, in the case of a phosphite, or tetrakis(2,4-di-t-butylphenyl) phosphonite, in the case of a phosphonite.
When a mixture of a phenol antioxidant and a phosphorus antioxidant is used, the mixed antioxidant is contained in the resin composition in an amount of 0.01 to 1 part by weight, in total, per 100 parts by weight of the total amount of component A and component B, and the mixture contains the phenol antioxidant (Ph) and the phosphorus antioxidant (P) at a proportion expressed as follows:
Ph: P=20:80 to 80:20 wt %, preferably from 20:80 to 60:40 wt %, and more preferably from 30:70 to 50:50 wt %.
When only a phenol antioxidant is used, although heat deterioration can be restrained, yellowing tends to occur. When only a phosphorus antioxidant is used, heat deterioration can be restrained by only a limited extent. The use of both phenol and phosphorus antioxidents makes it possible to obtain a synergistic effect, by which both heat deterioration and yellowing can be effectively restrained with a small amount of antioxidant added.
{circle around (2)} Anti-blocking Agent
A resin composition for extruded forms according to the present invention may preferably contain an anti-blocking agent for the purpose of preventing blocking and assuring the ability to open a formed film easily.
An anti-blocking agent used in the present invention may comprise one or more substances selected from among substances such as zeolite, synthetic silica, natural silica, talc, silicon dioxide, and amorphous aluminosilicate. Among these substances, zeolite, talc and amorphous aluminosilicate are preferable, and, more preferable are talc and amorphous aluminosilicate. A mixture of talc and either amorphous aluminosilicate or zeolite is particularly preferable.
An anti-blocking agent used in the present invention has an average grain size of not more than 10 xcexcm, preferably, not more than 5 xcexcm. Too great an average grain size causes some impairment in the transparency of a formed film.
An anti-blocking agent used in the present invention contains water in an amount of not more than 20% of the total weight thereof, preferably, not more than 10 wt %, and more preferably, not more than 5 wt %. Too great a water content causes foaming during formation, thereby making formation difficult.
{circle around (3)} Saturated- or Unsaturated-Fatty-Acid Amide (Slip Agent)
A resin composition for extruded forms according to the present invention may preferably contain a saturated- or unsaturated-fatty-acid amide (a slip agent) for the purpose of assuring easy-open ability of a formed film and preventing blocking.
A fatty acid amide used in the present invention comprises either a monoamide or bisamide of a saturated or unsaturated fatty acid. Specific examples of monoamides of saturated fatty acids which may be used, include palmitic acid amide, stearic acid amide, behenic acid amide, oxystearic acid amide, and methylol amide. Specific examples of usable monoamides of unsaturated fatty acids include oleic acid amide, erucic acid amide, linoleic acid amide, and ricinoleic acid amide. Specific examples of usable bisamides of saturated fatty acids include ethylenebisstearic acid amide, methylenebisstearic acid amide, and methylenebisstearobehenic acid amide. Specific examples of usable bisamides of unsaturated fatty acids include ethylenebisoleic acid amide, and methylenebisoleic acid amide.
Among these substances, preferable monoamides of saturated fatty acids are stearic acid amide, and behenic acid amide. Preferable monoamides of unsaturated fatty acids are oleic acid amide, and erucic acid amide. In the category of bisamides of saturated or unsaturated fatty acids, ethylenebisoleic acid amide is preferable. It is preferable to use a mixture of fatty acid amides in such a manner that a first component, comprising a monoamide of an unsaturated fatty acid, and a second component, comprising either a monoamide of a saturated fatty acid or a bisamide of a saturated or unsaturated fatty acid, are contained in the mixture at a proportion expressed as follows: first component:second component=80:20 to 20:80 wt %, preferably, from 75:25 to 60 to 40 wt %.
{circle around (4)} Amounts of Additives in Resin Composition
When an antioxidant, such as above, is contained as component C in a resin composition in according to the present invention, the antioxidant is contained in an amount within a range from 0.01 to 1 part by weight, preferably 0.03 to 0.5 part by weight, and more preferably from 0.05 to 0.2 part by weight, per 100 parts of the total amount of component A and component B also contained in the resin composition. Too small an amount of component C is not preferable because heat deterioration of the resin may occur, thereby making extrusion difficult during forming. Too large an amount of component C is not preferable either, because this may cause yellowing, cause bleedout, or impair heat sealability.
An anti-blocking agent, such as above, is contained as component D in the resin composition in an amount within a range from 0.01 to 1 part by weight, preferably from 0.1 to 0.8 part by weight, and more preferably from 0.3 to 0.7 part by weight, per 100 parts of the total amount of component A and component B. Too small an amount of component D is not preferable because a formed film is likely to suffer from blocking. Too large an amount of component D is not preferable either, because this may impair transparency.
A slip agent, such as above, is contained as component E in the resin composition in an amount within a range from 0.01 to 1 part by weight, preferably 0.03 to 0.5 part by weight, and more preferably from 0.05 to 0.2 part by weight, per 100 parts of the total amount of component A and component B. Too small an amount of component E is not preferable because a formed film may have poor slip properties. Too large an amount of component E is not preferable either, because those components of the resin which bleed out to the surface of a formed film may increase, thereby impairing heat sealability, etc.
Pellets obtained as described above may be suitably formed to produce a film or sheet.
Such a film may be produced by performing air-cooled inflation forming, two-stage air-cooled inflation forming, T-die film forming, water-cooled inflation forming, or the like, thereby obtaining a film which may be advantageously used as a wrapping or packaging material, etc.
A sheet may be produced by performing calendering, extrusion forming, compression molding, casting, or the like, thereby obtaining a sheet which may be advantageously used as a wrapping/packaging material, etc.